Radiotherapy operates by directing a beam of harmful radiation towards a tumour. To avoid causing unnecessary harm to the healthy tissue surrounding the tumour, the beam is collimated to a suitable cross-sectional shape and is directed towards the tumour from a variety of directions.
The apparatus for producing and controlling this beam has become steadily more complex and capable over time. Current external beam radiotherapy can now direct the beam towards the patient from a steadily rotating gantry while collimating the beam to a complex and varying cross-sectional shape that is tailored to deliver a varying dose rate to the patient to create a three-dimensional dose distribution that is maximised in the tumour, minimised in any nearby sensitive structures, and optimised in other tissue. Multiple-source radiotherapy apparatus is able to deliver precise doses to specific small volumes in the head and neck and upper shoulder areas of the patient and build these up to form similarly complex dose distributions by accurate indexing of the patient position.
To control these types of apparatus, treatment planning computers employ complex software to convert a desired dose distribution or a set of treatment constraints into a series of instructions for the physical movement and operation of the apparatus. These computers obviously need to know where the tumour is located; this information is obtained from internal scans of the patient, such as CT scans or the like.
This requires that a physician “segment” the scan, i.e. outlines the volume containing the tumour and volumes containing any sensitive structures such as the optic nerve, the digestive system, etc. Segmenting structures is therefore an important task in treatment planning applications, since the treatment planning process depends (inter alia) on the accuracy of segmentation for the quality of its results. There are many segmentation tools, spanning from completely manual ones to fully automatic ones.
The advantage of manual methods however is that they provide full (or at least much more) control over the result. The drawback is that it is very time consuming, difficult, and tedious to segment large 3D structures manually.
One drawback of many automatic methods—especially advanced ones—is the lack of control of the result. No method can be expected to be fully accurate in all cases, and when the result is not acceptable, there is often no way to correct it, or it must be corrected with purely manual tools—thereby cancelling some of the benefits of automatic methods.
Our GammaPlan™ and SurgiPlan™ tools currently provide manual outlining and a simple semi-automatic tool that works for certain images with good contrast, between target and background. These tools are useful, but could benefit from being more powerful.